The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
“Sensible cooling,” as that term is used in the field of heating/ventilation/air-conditioning (HVAC) is the removal of thermal heat from the air within an area, such as a room. “Sensible heat” load is thus heat load due to thermal heat in the air—i.e., the temperature at which the air is at. “Latent cooling” is the removal of moisture or humidity from the air. “Latent heat” load is thus the heat load due to moisture or humidity in the air.
With reference to FIG. 1, in a large room 10 where multiple air conditioning (A/C) units 12, 14 and 16 are used to cool the room, sensible heat flow (shown by heavy dashed lines) can tend to form into “zones” 18, 20 and 22 (indicated by heavy dotted lines 24). Although some heat can flow between zones (shown by light dashed lines 26), the majority of heat flow, which is controlled by convection, often stays within the zone determined by the air flow of the individual A/C units. Depending on the distribution of heat load in the room 10, this can cause an imbalancing of heat load between the A/C units 12, 14 and 16, with each A/C unit essentially assuming only the load in its own zone.
With reference to FIG. 2, latent heat (moisture) flow does not create this same “zoning” effect as sensible heat. Latent heat flow, although it can be partially affected by the air flow of the A/C units, will normally distribute evenly within the room space as indicated by dashed arrow 28. This is due to the effect of vapor pressure created by the moisture in the air. This vapor pressure will force the moisture to distribute evenly within the room 10 independent of the air flow of the A/C units 12, 14 and 16.
Due to the “zoning” effect of the sensible (or thermal) heat, the temperature control for the individual A/C units 12, 14 and 16 must be allowed to operate independently, with each unit providing the heat removal needed for its zone 18, 20 and 22 respectively. This is needed to ensure that proper temperature control maintained throughout the room 10. However, the humidity control for the individual A/C units 12, 14 and 16 is not restricted by this effect. In fact, since the moisture flows evenly within the room 10, any one A/C unit 12, 14 or 16 (or set of A/C units) can provide the total latent heat removal for the entire room and still maintain proper humidity control throughout the room.
FIG. 3 illustrates the standard method of performing temperature and humidity control. Due to thermal “zoning”, the sensible heat loads for each A/C unit 12, 14 and 16 are not equal. However, since moisture is evenly distributed throughout the room 10, the latent heat loads for each A/C unit 12, 14 and 16 are equal. Since moisture is removed from the space by performing cooling, any A/C unit 12, 14 or 16 that does not have adequate sensible load to cause the A/C unit to be cooling at a level necessary for the existing latent heat removal must provide more cooling than is needed for the sensible heat removal. In order to maintain temperature control, this necessitates the operation of heating (typically electric heating elements) in order to balance the extra cooling needed for humidity control.
In the example of FIG. 3, A/C unit 12 and A/C unit 16 are operating in an efficient mode since their respective sensible heat loads are larger than the latent heat load in the room 10. However, A/C unit 14 is not operating efficiently. It must operate at least at 50% sensible heat load in order to remove its share of the latent heat load in the room. But since its sensible heat load is only 20%, it must provide 30% heating to maintain proper temperature control in its zone.